Device for extraction of organic chemical compounds with toxic properties, which are present in atmospheric samples, by using solvents heated by the application of focalized microwaves in open systems (not pressurized)

ABSTRACT

Device to extract organic chemical compounds from particulate material (MP) that comes from atmospheric samples, using solvents heated by the application of focalized microwaves (MW), performed in open systems, which consists of:
         a magnetron;   an electronic control circuit of the magnetron;   a distillation flask that holds the solvent with the sample to be heated;   a filter for blocking microwaves, which allows getting out the vapor produced by the ebullition of the solvent with the sample to reach a reflux medium that allows condensing that vapor; and   a waveguide connected at one extreme with the magnetron and electronic control circuit, and at the other extreme with the distillation flask to be heated, the microwave blocking filter and the reflux medium.

FIELD OF THE INVENTION

The invention describes a device for extraction of organic chemical compounds with toxic properties such as Polycyclic Aromatic Hydrocarbons (PAHs) and Polychlorinated Biphenyls (PCBs), contaminants present in particulate material of atmospheric samples, which is carried out using solvents that have been heated by means of focalized microwaves (MW), performed in open systems (not pressurized).

BACKGROUND OF THE INVENTION

The employment of MW to extract organic compounds from particulate material (MP) resulting from air samples has been mainly used in applications of focalized MW in closed systems, however, the high pressures and temperatures reached in this type of equipments compel the development of very sophisticated, high safety and expensive equipments. One possibility to simplify and reduce costs is to use MW in open systems. The major problems in this type of applications are to achieve a good absorption of electromagnetic energy by the organic solvents, the regulation of the electromagnetic potency produced by the magnetron that generates the MW, and to limit MW leaks which can be injurious to the health of whom operate these equipments.

Organic solvents are required for the extraction. Most of the appropriate solvents for this purpose (e.g. hexane, toluene and others) have apolar characteristics which makes them impossible to heat using MW.

In the market there are two types of equipments for chemical extraction with MW, both of high cost, one pressurized and the other one open. In the open variety, the device is designed for its employment in the generation of specific chemical reactions (e. g. synthesis), where the high energies obtained by the MW are used. In this way, these devices have a very limited capacity for manipulation of equipment and glass material of traditional and standard use in the laboratory, because the MW leak blockage excessively restricts the transition (transit) zone of these components from the zone where the focalized MW to the exterior are generated. This problem obliges the use of glass material specially design for this purpose or the restriction of typical chemical procedures, such as reflux.

The trouble with the open variety of MW equipments is the possibility of producing excessive MW leaks, which can be controlled by limiting the size and shape of the orifices present in the metallic structures that guides and focalizes the MW in direction to the container that holds the sample to be heated and extracted, and in the zone of transition (transit) of the laboratory glass material from the focalized MW zone to the exterior.

The patent U.S. Pat. No. 6,061,926 (“Controlled energy density microwave-assisted processes”, from May 16^(th) 2000, by: Pare J R Jocelyn, Belanger Jacqueline M R and Punt Monique M.) describes the same principle of heating by absorption of MW, but restricted to small volumes of chemical solvents and transition (transit) zones, due to the need of limiting the leak of MW radiation. This equipment is designed and thought to carry out specific chemical reactions, such as synthesis of chemical compounds.

Consequently, it is required an equipment that could address those problems of restriction of heating by MW, rapidity, efficiency, volume, safety and use of standard chemical laboratory material.

Then, it is required a focalized microwave equipment (MWF) of an open variety, that could address those problems of restriction of heating by MW, rapidity, efficiency, volume, safety and use of standard chemical laboratory material.

SUMMARY OF THE INVENTION

The objective of the invention is to develop a device for rapid, efficient and secure chemical extraction, using solvents heated by the application of focalized microwaves in open systems (not pressurized). This extraction device is designed to be used in the extraction of organic chemical compounds with toxic properties, such as HAPs and PCBs, which are contaminants present in atmospheric samples.

The invention is designed to heat polar solvents like water, in such a way that when apolar solvents (e.g. hexane, toluene and others) are used like those typically utilized in the extraction of samples containing organic contaminants, it is necessary to add a portion of a polar solvent to the sample (e.g. acetone, isopropyl alcohol and others) with the purpose to achieve absorption of the MW and as a consequence rapid and efficient heating of the apolar solvent (toluene) until ebullition. The choice and proportion of polar solvent have been determined in such a way that when exposed to an oscillating electromagnetic field they absorb as much energy as possible as a result of molecular friction due to the rotation phenomena of themselves.

As one of the relevant aspects of this invention, it is also incorporated a novel filter designed to block the MW to the exterior, which allows an important increase of the transition zone from where the focalized MW (interior of the equipment) are generated to the place where the glass material typically used in the laboratory (exterior of the equipment) is connected, improving the extraction capacity, allowing the utilization and connection of equipments and glass material of traditional and standard use in the laboratory, and at the same time it allows the extraction using a larger volume of solvent by taking the advantage of the efficiency and rapidity of the heating using MWF. This filter for blocking MW leaks constitutes a characteristic that has not been found in the state of the art.

The working principle of the equipment is based on heating of substances, solvents in this case, due to the friction produced in the polar molecules, that is to say it is a mechanical effect induced by the oscillation of the electromagnetic field generated and canalized to the interior of the MW subsystem. The MW energy is generated by a magnetron, and it is then canalized by a waveguide to the glass container that holds the solvent, the waveguide and its termination are designed to achieve an optimal MW absorption, producing minimal reflection towards the magnetron. The filter for blocking the MW to the exterior allows that the energy delivered by the magnetron does not escape to the exterior and, as a whole with the waveguide, be efficiently absorbed by the heated solvent. The potency regulation is also an important aspect because it is required to maintain a condition of constant and moderate ebullition, this condition is accomplished by means of an electronic control specifically designed, which is programmed in a form that 100% of potency is initially applied to rapidly reach the ebullition state, and then a percentage close to 60% of work cycle is applied, and preferably, an approximate cadency of 1 Hz to maintain the process conveniently regulated.

The equipment works at a free frequency band of 2.450 MHz, using a magnetron of the type commonly found in domestic MW ovens of low cost, disposed in a waveguide especially design, in such a form that the container the holds the extraction solvent absorbs the maximum MW energy, which potency is controlled by means of the electronic control.

The developed equipment uses a magnetron of the type widely used in domestic MW ovens, which as a whole with the electronic and the specifically designed for this application MW focalization circuits translate into a product of moderate and very competitive cost compared to other market alternatives.

In summary, the objectives of the invention are to provide an equipment for rapid and efficient chemical extraction, using solvents heated by the regular application of electronically focalized MW performed in not pressurized open systems, with a magnetron of the type widely used in domestic MW ovens of low cost, and incorporating a filter for blocking MW to the exterior which allows using standard laboratory elements of much major capacity than similar equipments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general, complete and functional scheme of the proposed invention.

FIG. 2 shows a perspective view of the exterior of the whole equipment.

FIG. 3 shows a cut through a perspective view of the interior of the equipment.

FIG. 4 shows a complete perspective view of the equipment and the interior components.

FIG. 5 shows a lateral view of a detailed breakdown of all the component parts of the equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The developed equipment works at the free frequency band of 2,450 MHz, using a magnetron of the type widely used in domestic MW ovens of low cost, disposed in a waveguide especially design for this application, in such a form that the container the holds the extraction solvent absorbs the maximum MW energy, which potency is programmed and controlled by a specifically designed electronic circuit. The scheme of FIG. 1 shows the execution of the invention in a simple and functional form. The magnetron (102) generates the MW signal which potency is regulated by the electronic circuit (101), the MW is guided by the waveguide (103) to the standard glass container for the solvent (104), which correspond to a round bottom distillation flask with 250 ml capacity that holds the solvent to be heated (105) (extraction solvent). The vapor produced by the ebullition of the solvent ascends through the neck of the flask to the condenser of the reflux medium (107) and comes out from the interior of the MW equipment to the exterior through the filter for blocking the MW (106). The solvent in vapor phase is typically condensed in the reflux medium (107) and goes back to the distillation flask (104) to initiate a new reflux cycle.

The control of potency is achieved by varying the work cycle in an on/off feeding mode of the magnetron (102), but at substantially higher frequency (one cycle per second approximately) than the one used in the application of domestic ovens, because it is required an acceptable stability of temperature of the substances to be heated, which mass is considerably smaller in this application, compared to the typical mass in domestic ovens. The regulation of potency is initially at 100% until rapidly achieving ebullition, and then it is applied a percentage of work cycle close to 60% to keep the process regulated.

The waveguide (103) is designed according to the standard frequency of work specified in the literature, and its terminations (108 and 109) in the same manner, in order to achieve an optimal efficiency of transmission potency among the magnetron (102)-waveguide (103)-distillation flask (104).

The distillation flash (104) (e.g. a typical standard 250 ml round bottom flask) is disposed in the waveguide (103) termination, in such a way that almost all the solvent to be heated (105) is located inside the waveguide (103), and it behaves as an absorbent load. The distillation flask (104) is introduced in the waveguide (103) through a conductor mesh cylinder (110) which acts as an electromagnetic shield, but at the same time it allows visualizing the process from the exterior of the equipment through another window shielded with the conductor mesh (202) that can be appreciated in FIGS. 2 and 3. The exterior diameter of the distillation flask (104) that holds the solvent, is equal to the interior width of the waveguide (103) and to the interior diameter of the conductor mesh cylinder (110), in such a form that the solvent covers a maximum of the transversal section of the waveguide (103) to achieve maximum efficiency of heating, as can be appreciated in FIG. 1.

One of the key parts of the current invention is the safety device against MW leaks, a filter for blocking MW (106), which allows working with a standard distillation flask (104), a container with higher capacity than those used in the state of the art, and at the same time it constitutes a lid through which the distillation flask (104) is introduced into the conductor mesh cylinder (110) and waveguide (103) and taken out to the exterior of the MW equipment to load and unload solvent (105) in each process of extraction, as can be better appreciated in FIGS. 3 and 4.

The blocking filter for MW (106) is composed by a plurality of conductor plaques with cylindrical cavities or perforations through which passes the neck of the distillation flask (104). The circular conductor plaques have 0.5 mm width, with an exterior radius of 47 mm and an internal radius of 12 mm, disposed in parallel form and separated by 2 mm, and all connected through the exterior in short circuit, and open in the interior perimeter (zone of the neck of the distillation flask (104)). Between the open interior perimeter and the closed exterior perimeter in short circuit there is a distance of a quarter of a wavelength (30 mm) at the frequency of emission of the magnetron (102), in such a way that the perforations connected in short circuit in the exterior, transform into open circuits for the electromagnetic wave in the interior perimeter, where the neck of the distillation flask (104) passes, and as a consequence it rapidly attenuates before reaching the exterior. In FIGS. 2, 3 and 4 can be appreciated the conductor plaques that form the cavities of the blocking filter for MW (106).

It is worth mentioning that excessive leaks of MW approximately greater than 0.5 mW/cm² constitute a risk for the operator health, according to the Chilean legislation. The invention, incorporating the blocking filter for MW (106) which has been designed to practically annul the MW to the exterior, allows an experimental attenuation of approximately 20 dB in relation to not using the filter. Considering the maximum potency of MW available and needed in the magnetron (102) (approximately 800 W), this important reduction of MW leaks allows the equipment to work far below the threshold previously mentioned, a condition not met when the MW blocking filter (106) is not used. Without the filter, under the previous condition, the radiation to the exterior is ten times the minimum considered acceptable.

In regard to the velocity of solvent heating until reaching an ebullition condition, there have been obtained averages times close to one minute in multiple essays, which are much shorter than those obtained with equipment for conventional heating by convection, being those times close to 25 minutes considering the same volume of solvent (e.g. toluene).

The fan (301) is used to counterbalance the inevitable heating of the magnetron (102), whose ventilation is accomplished through the metallic mesh window (202). 

1. A Device for extracting organic chemical compounds from material in particle form (MP) from atmospheric samples that uses solvents heated by the application of focalized microwaves (MW) in open systems comprising: a magnetron, where the magnetron has a frequency of emission; an electric control circuit of the magnetron; a distillation flask, where the distillation flask comprises a solvent with a sample to be heated; a microwave blocking filter, where the microwave blocking filter enables vapor produced by the ebullition of the solvent with the sample reaching a reflux medium to exit thereby causing the vapor produced by the distillation to condense; and a waveguide, which has in one end the magnetron and the electric control circuit, and in the other end the distillation flask to be heated, the microwave blocking filter and the reflux medium, wherein said microwave blocking filter comprises a plurality of circular conductor plates, each with a central hole, in such a way that the plates constitute a cylindrical cavity in the microwave blocking filter's center through which the neck of the distillation flask is allowed to pass through, where said plates are disposed in parallel positions and connected in the exterior in short circuit, and where the distillation flask is open in the interior perimeter of the zone of the neck of the distillation flask; where between the open interior perimeter and the closed exterior perimeter in short circuit, there is a distance of a quarter of a wavelength (l/4) at the frequency of emission of the magnetron, whereby the cylindrical cavities between the conductor plates ending in short circuit in the exterior transform into open circuits for an electromagnetic wave in the interior perimeter, and as a consequence, the electromagnetic wave rapidly attenuates and is blocked before reaching the exterior.
 2. The device for extracting organic chemical compounds according to claim 1, wherein each circular conductor plate of the plurality of circular conductor plates has approximately 0.5 mm of thickness, with an exterior radius of approximately 47 mm and an internal radius of approximately 17 mm.
 3. The evice for extracting organic chemical compounds according to claim 2, wherein each circular conductor plates of the plurality of circular conductor plates disposed in parallel position are separated approximately by 2 mm between each other.
 4. The device for extracting organic chemical compounds according to claim 1, where the magnetron comprises a power source, where the power source has a working cycle, wherein different power levels are achieved by varying the working cycle in on/off mode of the power source of the magnetron with a frequency of approximately one cycle per second.
 5. The device for extracting organic chemical compounds according to claim 1, wherein the microwave blocking filter acts as a top of a conductor mesh cylinder which electromagnetically shields the distillation flask for heating while at the same time allowing the process to be viewed from the exterior of the equipment through another window shielded with a conductor mesh, where the conductor mesh cylinder has an interior diameter, where the distillation flask has an exterior diameter, where the waveguide has an interior width, where the exterior diameter of the distillation flask is equal to the interior width of the waveguide as well as to the interior diameter of the conductor mesh cylinder whereby the solvent covers a maximum of a transversal section of the waveguide to achieve maximum efficiency of heating.
 6. A method of operation of a device for extracting organic chemical compounds from material in particle form (MP) from atmospheric samples comprising the steps of: a) providing a device for extracting organic chemical compounds from material in particle form (MP) from atmospheric samples where the device comprises: i) a magnetron, where the magnetron has a power, where the power can be regulated, where the magnetron comprises a power source, where the power source has a working cycle that can be varied, where the working cycle has an on/off mode; ii) an electric control circuit of the magnetron; iii) a distillation flask, where the distillation flask comprises a solvent with the a sample to be heated; iv) a microwave blocking filter, where the microwave blocking filter enables vapor produced by the ebullition of the solvent with the sample reaching a reflux medium to exit thereby causing the vapor produced by the distillation to condense, wherein said microwave blocking filter comprises a plurality of conductor plates, each with one central hole, in such a way that the plates constitute a cylindrical cavity in the microwave blocking filter's center which the neck of the distillation flask is allowed to pass through, where said plates are disposed in parallel positions and connected in the exterior in short circuit, and where the distillation flask is open in the interior perimeter of the zone of the neck of the distillation flask; where between the open interior perimeter and the closed exterior perimeter in short circuit there is a distance of a quarter of a wavelength (l/4) at the frequency of emission of the magnetron, whereby the cylindrical cavities between the conductor plates ending in short circuit in the exterior transform into open circuits for an electromagnetic wave in the interior perimeter, and as a consequence the electromagnetic wave rapidly attenuates and is blocked before reaching the exterior; and v) a waveguide, which has in one end the magnetron and the electric control circuit, and in the other end the distillation flask to be heated, the microwave blocking filter and the reflux medium; b) controlling the regulation of the magnetron power by varying the working cycle in on/off mode of the power source of the magnetron, where the frequency is approximately one cycle per second; c) setting the power of the magnetrong to 100%, where the power is left at 100% until ebullition is reached; d) setting the power source of the magnetron to approximately 60%, for maintaining the process regulated; e) extracting, in ebullition, the organic chemical compounds found in the MP from atmospheric samples; f) allowing the vapor to reach the reflux medium which allows condensing the vapor produced by the distillation; g) allowing the evaporated solvent to exit the inside of the MW equipment to the exterior through the MW blocking filter and returning to the distillation flask by condensation to initiate the reflux cycle again. 